1. Field of the Invention
This invention relates to improvements in chipper knives and knife holder assemblies.
2. Description of the Prior Art
Chippers are machines capable of chipping various sizes and types of wood species into particles known generally as chips. The chips are used, primarily, as raw material for pulp manufacturing.
The wood species that are cut into chips for pulp production vary greatly in size and type, i.e. some woods are very hard and some are very soft.
There are two broad areas of chip production: primary chip manufacturing where chips are cut out of whole log trunks, and secondary chip manufacturing where chips are produced from residual wood, i.e. trimmings from sawmills.
In recent years, disposable or reversible knives have gained acceptance in the industry, but such acceptance has been limited to the secondary chip manufacturing process. Most secondary chipping is done in smaller chippers and the wood is usually softwood in the form of slabs. Thus, the demands or stresses on such knives is less then the demands made on the nonreversible, re-grindable knives used in the primary chip manufacturing process.
Specifically, the knives in the secondary chipping industry have not gained acceptance in the primary chipping industry primarily due to the designs of the knife holder assemblies. The known designs provide very limited clamping area, i.e. only a small part of the surface area of the knife is actually clamped. Thus, a knife having utility in a softwood chipper will fail prematurely when used in a high density hardwood chipper.
More particularly, the known reversible knives are subject to over-torquing when the clamp that holds the knife is tightened down. Due to the small surface area between the knife and the clamp, the clamp springs down more than anticipated and the clamping force is concentrated on the lower heel of the knife at the clamp contact surface abutting the knife. Thus, the upper part of the clamping surface is subjected to a decreased clamping pressure and functional problems occur. For example, wood fibers can enter into the space between a poorly clamped knife and its counter knife, thereby further degrading the performance of the knife.
At the time the present invention was made, it was not obvious to those of ordinary skill in this art how a reversible blade suitable for use in chipping high density whole log trunk hardwood could be developed.